Reliability, validity and responsiveness of the squares test for manual dexterity in people with Parkinson's disease.

Objective: Impaired manual dexterity is one of the major disorder in people with Parkinson's Disease (PwPD). However, there is limited research examining the measurement properties, especially the validity and responsiveness of the tools used to assess manual dexterity. The aim of this study was to examine reliability, validity, and responsiveness of the Squares Test (ST) in PwPD.
Patients and Methods: Fifty-seven PwPD and 50 healthy people, all of whom were right-handed, were recruited. The ST, Nine-Hole Peg Test, Unified Parkinson's Disease Rating Scale (UPDRS), and Hoehn and Yahr scale were performed in ON state. For responsiveness analysis, the ST and UPDRS motor score (UPDRS-III) were also performed in OFF state.
Results: The ST showed excellent test-retest reliability. The ST was found to correlate significantly with other outcome measures, which indicated good concurrent validity. PwPD demonstrated significantly lower scores of the ST than healthy people, which demonstrated satisfactory known-groups validity. The ST had excellent discriminant validity. The ST scores of 52 for more affected hand and 62 for less affected hand were shown to best discriminate between PwPD and healthy people. The ST is high internal responsiveness based on standardized effect size and standardized response mean (0.79 and 1.88, respectively for more affected hand and 0.85 and 1.83, respectively for less affected hand), and also PwPD had better performance based on the ST in ON state than in OFF state (p < 0.001 for both hands). Moderate correlations were found between the change scores of the ST and UPDRS-III, which reflected adequate external responsiveness.
Conclusions: The ST is a reliable, valid and responsive measurement tool for assessing manual dexterity in PwPD.
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